Memory Map of the HPC167064

Functional Modes of Operation (Continued)

Security Level 2

This security level prevents programming of the on-chip EPROM or the ECON registers thereby providing WRITE protection. Read accesses to the on-chip EPROM or ECON registers may be accomplished without constraint in EPROM. Read accesses to the on-chip EPROM may be accomplished without constraint in NORMAL RUNNING mode.

Security Level 1

This security level prevents programming of the on-chip EPROM or ECON registers—thereby providing registers write protection. Read accesses to the on-chip ECON-regis- ters may be accomplished without constraint in EPROM mode. Read accesses to the on-chip EPROM will produce ENCRYPTED data in EPROM. READ accesses to the on- chip EPROM, during NORMAL RUNNING mode, are sub- ject to Runtime Memory Protection. Under Runtime Mem- ory Protection, only instruction opcodes stored within the on-chip EPROM are allowed to access the EPROM as oper- and. If any other instruction opcode attempts to use the contents of EPROM as an operand, it will receive the hex value ‘‘FF’’. The Runtime Memory Protection feature is de- signed to prevent hostile software, running from external memory or on-chip RAM, from reading secured EPROM data. Transfers of control into, or out of the on-chip EPROM (such as jump or branch) are not affected by Runtime Mem- ory Protection. Interrupt vector fetches from EPROM pro- ceed normally, and are not affected by Runtime Memory Protection.

Security Level 0

This security level prevents programming of the on-chip EPROM or ECON registers, thereby providing write protec- tion. Read accesses to the on-chip ECON registers may be accomplished without constraint in EPROM mode. READ accesses to the on-chip EPROM are NOT ALLOWED in

An erasure system should be calibrated periodically. The distance from lamp to unit should be maintained at one inch. The erasure time increases as the square of the distance. (If distance is doubled the erasure time increases by a factor of 4.) Lamps lose intensity as they age. When a lamp is changed, the distance has changed or the lamp has aged, the system should be checked to make certain full erasure is occurring.

Incomplete erasure will cause symptoms that can be mis- leading. Programmers, components, and even system de- signs have been erroneously suspected when incomplete erasure was the problem.

Minimum HPC167064 Erasure Time

Light Intensity	Erasure Time
(Micro-Watts/cm2)	(Minutes)
15,000	36

10,000	50

The HPC167064 has 256 bytes of on-chip user RAM and chip registers located at address 0000 – 01FF that is always enabled, and 256 bytes of on-chip RAM located at 0200 – 02FF that can be enabled or disabled. It has 8 kbytes of on- chip EPROM located at address 0E000 – 0FFFF that is al- ways enabled and 8 kbytes of EPROM located at address 0C000 – 0DFFF that can be enabled or disabled.

The ECON6 contains two bits ROM0 and RAM0. When these bits are ‘‘1’’ (erased default), full 16 kbytes of ROM and 512 bytes of RAM are enabled. Programming a ‘‘0’’ to these bits disables the lower 8k for the EPROM and upper 256 bytes for the RAM. The ECON registers are only acces- sible to the user during EPROM mode.

EPROM mode. Such accesses will return data value ‘‘FF’’ hex. Runtime Memory Protection is enforced as in security level 1.

These four levels of security help ensure that the user EPROM code is not tampered with in a test fixture and that code executing from RAM or external memory does not dump the user algorithm.

Erasure Characteristics

The erasure characteristics of the HPC167064 are such that erasure begins to occur when exposed to light with wave- lengths shorter than approximately 4000 Angstroms (—). It should be noted that sunlight and certain types of fluores- cent lamps have wavelengths in the 3000— – 4000— range.

After programming, opaque labels should be placed over the HPC167064’s window to prevent unintentional erasure. Covering the window will also prevent temporary functional failure due to the generation of photo currents.

The recommended erasure procedure for the HPC167064 is exposure to short wave ultraviolet light which has a wave- length of 2537 Angstroms (—). The integrated dose (i.e., UV intensity c exposure time) for erasure should be a minimum of 30W-sec/cm2.

The HPC167064 should be placed within 1 inch of the lamp tubes during erasure. Some lamps have a filter on their tubes which should be removed before erasure. The era- sure time table shows the minimum HPC167064 erasure time for various light intensities.

Address In

EPROM Mode

7FFF

4000

3FFF

2000

1FFF

0000

Address In Other HPC Modes

Operation

FFFF

E000 –

DFFF

Enabled or Disabled by config logic

C000